PARTI CHAZYAN AND RELATED BRACHIOPODS—COOPER 487 
moderately convex, somewhat flat topped and with short, steep lateral slopes ; 
umbonal region swollen; sulcus shallow and broad, originating about 5 mm. 
anterior to the beak; flanks bounding sulcus gently swollen; umbonal slopes 
to the cardinal extremities steep. Interarea long, catacline, but with strongly 
and narrowly incurved beak. 
Brachial valve strongly convex and with the greatest convexity in the pos- 
terior half ; anterior half sloping moderately to the pedicle valve ; umbonal region 
strongly convex ; beak strongly incurved and overhanging the pedicle interarea ; 
median region broadly sulcate, sulcus originating anterior to the umbo, broad 
and shallow, poorly defined at the front margin. Lateral slopes short and steep. 
Measurements in mm.—Holotype, length 13.8, brachial length 13.3, width 17.2, 
hinge width 13.5, thickness 11.3. 
Type.—Holotype: 110792. 
Horizon and locality—Probably Valcour formation in New York: On Val- 
cour Island, Lake Champlain, Plattsburg (15’) Quadrangle. 
Discussion.—This species is similar in ornamentation to M. transversa but 
differs markedly in having both valves much more tumid and in being much less 
transverse. The interarea is longer and the beak narrower than M. transversa, 
and the brachial valve has a more strongly arched umbonal region. Mimella 
valcourensis is a rare species; only a single specimen is now known. 
MIMELLA VIRGINIENSIS Cooper, new species 
Plate 37, B, figures 5-7; plate 91, H, figures 35, 36 
Mimella sp. Butts, Virginia Geol. Surv. Bull. 52, p. 43, pl. 73, figs. 47-52, 1942. 
Shell large, wider than long, with well-rounded sides and gently rounded 
anterior margin. Hinge narrow; anterior commissure very gently uniplicate. 
Surface multicostellate, costellae numbering 10 to 5 mm. at the front margin. 
Pedicle valve fairly evenly and gently convex in lateral profile but with an- 
terior somewhat flattened. Anterior profile broadly and moderately convex. 
Umbonal and median regions swollen; anterior region gently inflated except for 
median quarter which is depressed to form a shallow sulcus. Posterolateral 
slopes somewhat inflated but steeply inclined to the cardinal extremities. Inter- 
area long, apsacline; beak very gently incurved. 
Brachial valve strongly convex in lateral profile and with the maximum con- 
vexity at about the middle; anterior profile strongly arched, with steep and long 
lateral slopes. Whole median region and umbo strongly swollen. Lateral slopes 
long and steep. Interarea short. 
Measurements in mm.—Holotype, length 18.5, brachial length 17.2, width 22.6, 
hinge width 16.8, thickness 12.9. 
Types.—Holotype: 98188a, figured paratype: 110694; unfigured paratypes: 
98188b-e. 
Horizon and locality.—Whistle Creek formation in Virginia: 14 miles north- 
west of Lexington, Lexington (15’) Quadrangle; top of the ridge 1,000 feet 
